Double hologram

ABSTRACT

The invention relates to a method of providing an article with identifying information, in which a hologram is provided from which at least first and second hologram patterns separated physically from each other can be reproduced. In this case, provision is made for the hologram to be produced in such a way that the first and second hologram patterns can generally be reproduced in one and the same direction but in different planes.

The present invention relates to how identifying can be provided byholograms.

Holograms are already generally common nowadays. In order to be able toidentify articles, for example as authentic, there are simple hologramson check cards, identity cards, external packaging, such as forsoftware, entry cards and the like. One problem with conventionalholograms is that the holograms often provide security against forgerywhich is inadequate. Furthermore, the identifying information is oftennot precise enough in order to identify an individual article, forexample.

It has already been proposed to provide holograms on articles, thehologram having a hologram-bearing area which is provided withinterference patterns which form a holographic image, and it beingpossible for different holographic images to be produced in differentdirections. This, requires light to be radiated in from two differentdirections and, possibly, for the images to be combined. In this case,the expenditure on apparatus is undesirably high.

The object of the present invention is to provide an innovation forcommercial application.

This object is achieved by using the features specified in theindependent claims. Preferred embodiments will be found in thesubclaims.

The invention thus proposes, firstly, a method of providing an articlewith identifying information, in which a hologram is provided, fromwhich at least first and second hologram patterns separated physicallyfrom each other can be reproduced, the hologram being formed in such away that the first and second hologram patterns can generally bereproduced in one and the same direction but in different planes.

A first important basic finding of the present invention is to be seenin the finding that particularly expedient identifying information canbe provided by hologram patterns being produced in different planes. Inthis case, it has been recognized that the projected hologram in thefirst plane does not have to significantly disrupt the reproduction ofthe hologram pattern separate from this in the second plane if thereading planes are located sufficiently far from each other. As a resultof this finding, it has become possible to permit the identification ofan article by means of first and second holograms even when light isradiated in from a single direction and, to be specific, even in caseswhere the area for the hologram can only be small.

In a preferred variant, at least one of the hologram patterns is amachine-readable code. Such a code can, if appropriate, be structured insuch a way that its presence cannot readily be detected, for examplewith the naked eye, even if a projection screen is accidentally movedinto the correct plane. This makes it possible to provide on the articleidentifying information whose presence cannot readily be established.

Provision can further be made for one of the hologram patterns torepresent a pattern which can be registered visually. This isadvantageous, since the simplest possible article identification istherefore permitted. It should be pointed out that there can be morethan just a first and a second hologram pattern that can be reproducedin different planes.

The hologram can be provided on a hologram substrate in such a way thatfirst and second mutually separated regions are provided on thehologram-bearing area. In this case, the subregions used in the firstand second hologram pattern can be interleaved with each other in themanner of a checkerboard or combined with each other in a different way.

A combination of this type, in which the information for the first andsecond hologram pattern is distributed in total over a larger region,already contributes to increasing the scratch resistance and protectionagainst damage.

However, it is preferred for a single region to be provided for thefirst and second hologram patterns and possibly also for furtherhologram patterns. This region then bears an interference pattern, fromwhich the different hologram patterns in the different planes may beprojected. The determination of suitable such interference patterns perse is known. The iterative calculation of the interference pattern whichprovides the hologram is preferred. In this context, reference is made,merely by way of example, to the article “Fresnel ping-pong algorithmfor two-plane computer-generated hologram display” by R. G. Dorsch etal., in Applied Optics, vol. 33, No. 5, page 869 ff.

The interference pattern of the first hologram is preferably determinedin such a way that the first and second hologram patterns lie so farapart from each other that they can be read out with different readingmeans. These different reading means can then, for example, receivelight reflected or transmitted through a beam splitter. In analternative, it is possible to hold a single reading means, for examplea projection screen, such that it can be displaced between the twoplanes.

The hologram itself is preferably produced as a computer-generatedhologram by using a single write beam. The article-characterizinginformation which is provided can be individually characterizinginformation, such as a portrait of the user of the article, an address,medical data or, for example in the case of a technical article,information which relates to its manufacture.

The write beam can in particular be a laser beam. The use of a doublebeam from a material, in particular a beam which pre-illuminates over alarge area, and a beam which writes point by point in the regionpre-heated, for example, by the pre-illumination, is possible.

The hologram can be impressed into a substrate, in particular if aseries of articles is to be provided with items of identifyinginformation identical to one another. In the case of interleaving, firstparts can be pre-impressed, while other parts can be writtenindividually.

The invention relates further to an apparatus for reading a hologramcontaining identifying information, such as emerges in particular fromone of the method claims, the apparatus comprising a reading lightsource for the reproduction of the at least first hologram pattern inthat direction in which the second hologram pattern can also bereproduced. Therefore, only a single reading light source is requiredfor the reproduction of the two hologram patterns.

In the case of the apparatus, at least one hologram-pattern reproductionmeans can be fixedly provided, it being possible for this to be, inparticular, a projection screen. Furthermore and/or alternatively, aphotosensitive field, in particular a CCD, can be provided, in order inparticular to register a hologram pattern representing machine-readablecode in or close to its focal plane.

If a photosensitive field is provided, it is preferred for the apparatusto comprise a data processing unit, in order to evaluate the patternregistered by the photosensitive field directly in the apparatus.

Protection is also desired for a data medium having an area toaccommodate a hologram as claimed in one of the method claims and,respectively, also the use of a data medium to accommodate such ahologram. Particularly suitable data media comprise a polymer material,into which the hologram is introduced. The polymer material can be apre-oriented polymer material, in particular pre-oriented polypropylene.The article safeguard is produced separately from the article and thenarranged on the latter.

The invention will now be described below by way of example, using thedrawing, in which:

FIG. 1 shows a sketch relating to reading a hologram according to theinvention.

According to FIG. 1, a reader designated generally by 1 for reading ahologram 2 on a hologram substrate which belongs to an article 3,comprises an individual laser 4, whose light beam 5 is deflected ontothe hologram 2 by means of suitable optics 6 a, 6 b, the diffractedlight of first order, differing from the light of the zeroth order,passing through optics 8 here, which improves the signal/noise ratiowhen receiving the diffracted light by means of the early delimitationof the light of zeroth order, but which is not absolutely necessary perse.

The hologram 2 is a computer-generated hologram produced with asingle-beam writing device. The interference pattern of the hologram 2is chosen such that two sharp but different hologram patterns areproduced at two different distances from the hologram substrate 3.

The article 3 in the present case is a check card, on which a region ofpre-oriented polymer is provided, which bears the hologram 2. The,interference pattern of the hologram in this case extends over theentire area of the hologram substrate.

The laser 4 emits visible light. The visible light is collimated by thelens 6 a and radiated in onto the hologram 2 at an oblique angle by adeflection mirror 6 b. The oblique irradiation is carried out in such away that the main reflection of light diffraction of zeroth order 7 doesnot fall into the further optical arrangement 8 for determining the twohologram patterns encoded in the hologram.

The optics 8 comprise a beam splitter 8 a, which is arranged in thatdirection in which the light diffracted in the first order by thehologram 2 enters.

At a first distance a from the beam splitter 8 a there is in thetransmission light path a projection screen 8 b, the distance a beingchosen such that the first hologram pattern is imaged sharply on theprojection screen. In addition, in the reflection light path for thelight reflected by the beam splitter, there is a CCD array 8 c which isarranged at the distance b and which is connected to a detection unit(not shown) for the identification of a machine-readable code. Theoptical path lengths a and b are different.

The reader 1 is used as follows:

First of all, the article 3 bearing the hologram 2 is arranged with thehologram 2 at the envisaged position and illuminated by the laser 4. Thefirst hologram pattern is then inspected visually on the projectionscreen 8 b, as indicated by the eye 9.

At the same time, without a further laser light source being required,the second hologram pattern is registered on the CCD 8 c, and themachine code projected as a result is decoded and checked for itsinformation content.

The advantage with the arrangement is that merely viewing the hologram,even when the first, optically visible hologram pattern is produced,does not permit the fact that a further, machine-decodable hologrampattern is present to be detected.

It should be pointed out that more than two hologram patterns can beencoded; in particular in more than two planes. It should be mentionedthat, in addition to visible light, invisible light, in particular fromIR laser diodes, is also used.

1. A method of providing an article with one polymer area bearing ahologram as identifying information comprising: calculating one computergenerated hologram such that at least two sharp patterns can bereproduced therefrom at different distances but into a same direction;and writing the computer generated hologram in the polymer area usingone single light beam writing device.
 2. The method of claim 1, whereinthe polymer area comprises two mutually separated regions interleavedwith each other.
 3. The method of claim 2, wherein first interleavedregions are impressed while other regions are written using the singlelight beam writing device.
 4. The method of claim 3, wherein thecomputer generated hologram is calculated such that the two sharppatterns lie so far apart from each other that the patterns can be readsimultaneously with different reading means.
 5. The method of claim 4,wherein said calculating step comprises iteratively determining aninterference pattern from which the two, different sharp patterns can bereproduced.
 6. The method of claim 3, wherein said calculating stepcomprises iteratively determining an interference pattern from which thetwo, different sharp patterns can be reproduced.
 7. The method of claim2, wherein the computer generated hologram is calculated such that thetwo sharp patterns lie so far apart from each other that the patternscan be read simultaneously with different reading means.
 8. The methodof claim 7, wherein said calculating step comprises iterativelydetermining an interference pattern from which the two, different sharppatterns can be reproduced.
 9. The method of claim 2, wherein saidcalculating step comprises iteratively determining an interferencepattern from which the two, different sharp patterns can be reproduced.10. The method of claim 1, wherein the two sharp patterns comprise afirst hologram pattern and a second hologram pattern, and wherein thepolymer area comprises one single region bearing one interferencepattern written by the single light beam writing device for both thefirst and the second hologram patterns combined.
 11. The method of claim10, wherein the computer generated hologram is calculated such that thetwo sharp patterns lie so far apart from each other that the patternscan be read simultaneously with different reading means.
 12. The methodof claim 10, wherein said calculating step comprises iterativelydetermining an interference pattern from which the two, different sharppatterns can be reproduced.
 13. The method of claim 1, wherein thecomputer generated hologram is calculated such that the two sharppatterns lie so far apart from each other that the patterns can be readsimultaneously with different reading means.
 14. The method of claim 13,wherein said calculating step comprises iteratively determining aninterference pattern from which the two, different sharp patterns can bereproduced.
 15. The method of claim 1, wherein said calculating stepcomprises iteratively determining an interference pattern from which thetwo, different sharp patterns can be reproduced.
 16. The method of claim1, wherein the polymer comprises a pre-oriented polymer.
 17. The methodof claim 1, wherein the article is provided with the polymer area afterthe computer generated hologram is written into the polymer.
 18. Themethod of claim 1, wherein at least one pattern of the two sharppatterns is a machine decodable hologram pattern.
 19. The method ofclaim 1, wherein at least one pattern of the two sharp patterns can beregistered visually.
 20. The method of claim 1, wherein informationidentifying the article individually is provided.